Essential features of the operation of such switches are high reliability and tolerance of faults. Providing redundant hardware is only a part of fault tolerance. It is also necessary to determine the nature of any problem that occurs with the main hardware and to make the best use of the redundant hardware in the circumstances.
Published UK patent application No 2271041 discloses a switch in which a control means monitors the operation of the switch and adapts the switching in accordance with a stored list of instructions upon detection of a predetermined condition. This may be, for example, time or data traffic conditions or a fault in one of the data links.
As an example, where the switch contains a main communications controller and a spare controller, the switch may be programmed to use the spare controller if the main controller fails. However, there are several possible disadvantages with this. For example, it may be that the controller is not itself faulty, but the link to it has failed. There is also no provision for dealing with the problem of the spare controller also failing. If the main controller (or its link) recovers, should communications be returned to it from the spare. Should the Network Management System be notified of the switch-over from one controller or link to the other. The answers to these questions will depend on the situation. For example, if the spare controller uses an expensive "pay on usage" public data circuit to provide a back-up for the main "leased line", it will be desirable to return to the main line as soon as possible. But if the service carried is such as to demand high reliability, for example video coverage for remote surgery, it will be necessary to delay switching back to the main line until there is no risk of further disruption to the service.
The present invention provides a network switch which can be configured to provide heuristic solutions to management problems within the network components.